In a current process of measuring a fault point in a radio frequency system by using a scanning rangefinder, a series of test signals are usually transmitted into the radio frequency system. The test signal is reflected after arriving at the fault point. Accordingly, a receiver receives a spectrum signal obtained by reflecting by the fault point. Then a transmission delay d between transmission and reception of the test signal is estimated according to a curve chart of a time-domain signal corresponding to the received spectrum signal. A distance s between a transmitter and the fault point is obtained after the transmission delay d is multiplied by a radio wave speed V and then divided by 2. However, currently, a curve in the curve chart of the time-domain signal corresponding to the received spectrum signal is often deformed or has an obvious distortion. Consequently, accuracy of detecting the fault point is severely affected.